This Month’s Sky – March 2017

What’s Up in the Sky
AAA Observers’ January Guide
By Tony Faddoul

March’s Evening Planets: Bright Venus will be in Pisces the Fish until around 8 PM in the first 3 weeks of March, while Mercury will be in in Pisces until around 8 PM in second half of the month. Mars will be between Pisces and Aries the Ram until about 10 PM. Jupiter will be in Vir-go the Maiden all night as of 8 PM. Find Uranus in Pisces until 8 PM.

March’s Evening Stars: The Winter Triangle will be up in March until around midnight with Sirius, the brightest star viewed from Earth in Canis Major the Great Dog, Betel-geuse in Orion the Hunter, and Procyon in Canis Minor the Small Dog. Spot Rigel in Orion, Capella in Auriga the Char-ioteer, Aldeberan in Taurus the Bull, and bright Castor and Pollux in Gemini the Twins. Also find the stars of constella-tions Cassiopeia, Perseus, Draco, Virgo, Leo, and Ursa Major and Ursa Minor (the Big and Little Dippers).

March’s Morning Planets: Venus will be in Pisces until around 6 AM in the last week of March. Jupiter will be in Virgo until sunrise. Saturn will be in Ophiuchus the Ser-pent Bearer after 2 AM and until sunrise.

March’s Morning Stars: Spot the Summer Triangle of Vega in Lyra the Harp, Deneb in Cygnus the Swan, and Al-tair in Aquila the Eagle as of 3 AM and earlier every night. Look for reddish Antares in Scorpius the Scorpion, Arcturus in Boötes the Herdsman, and Spica in Virgo, along with the stars of constellations Leo, Hercules, Libra, Sagittarius, Cas-siopeia, Corvus, Draco, and the two Dippers.

March “Skylights”

Mar 3 Moon at perigee (229,325 miles away)

Mar 4 Moon occults Aldebaran 11:10 PM EST

Mar 5 First Quarter Moon at 6:30 AM EST

Mar 12 Full Moon at 10:53 AM

Mar 18 Moon at apogee (251,440 miles away)

Mar 20 Vernal Equinox

Last quarter moon at 11:58 AM

Mar 27 New Moon at 10:55 PM

Mar 30 Moon at perigee (226,100 miles away)

How Earthy are the 7 New Earths?

The February announcement of seven Earth-like exoplanets in a star system less than 40 light-years away has offered a world of worlds to investigate. Host star TRAPPIST-1a is a very small and dim red dwarf, and its planets are very close to the star and to each other. All are rocky and about Earth’s size and weight. Three of them are considered to be in the habitable zone, where liquid water may exist on the surface and support life. While no direct observations have been made, scientists can estimate temperature, density, and surface conditions, based on information collected from transit photometry, to help us picture these possible Earths.

What is the Habitable Zone?

The habitable zone defines an orbital distance from a star where a planet can support liquid water, depending on its surface temperature and atmospheric pressure. In other words, carbon-based life (as we know it on Earth) could survive there. We know something about the TRAPPIST-1 planets’ temperatures, while atmospheric studies are ongoing.

TRAPPIST-1a is an ultra-cool dwarf star. It is only 8% of the mass of the Sun and 11% of its radius; 750,000 TRAP-PIST-1a-sized stars could fit inside our Sun. Its temperature is only 2550 K, compared to the 6000 K on the Sun.

TRAPPIST-1b is the closest planet to the star, but it is much closer than the Earth is to the Sun. It is so close that it can complete a full orbit around its star in just one and a half days. Its radius is 9% larger than Earth’s, and it weighs 85% of our Earth’s mass.

TRAPPIST-1c takes about two and a half days to complete its orbit. Its radius is 6% larger than the Earth’s, and it’s the heaviest planet, with 38% more mass than the Earth.

TRAPPIST-1d has a radius 77% the size of Earth’s. It com-pletes its orbit in four days and is 41% the mass of Earth.

TRAPPIST-1e completes its orbit in about 6.1 days, and its radius is 92% of Earth’s. It is very close in size to our neigh-bor planet Venus. It is 32% lighter than Earth.

TRAPPIST-1f is the closest in size to Earth, with a radius that is 4% larger than that of our planet. It completes its orbit in 9.2 days and is 2/3 the mass of our Earth.

TRAPPIST-1g takes 12 days to complete its orbit. It is the largest planet in the system with a radius 13% larger than Earth’s. It weighs 34% more than Earth.

TRAPPIST-1h is the smallest and furthest from its star. However, this seventh planet is much closer to its star than Mercury is to the Sun, about seven times closer. It takes 20 days to orbit, and its radius is 75% the radius of Earth.

How do these planets actually look?
The images published for the seven planets, and the rest of the exoplanets, are imaginary depiction done by artists. None of the known exoplanets has been seen, or photographed, with optical telescopes. The information we got are mostly collected using transit photometry.